Much of the nation was naturally focused on President Barack Obama as he announced his drawdown schedule for U.S. troops in Afghanistan.

But the experts on the region were actually looking elsewhere — at Afghanistan’s neighbor, the unstable, nuclear-armed Pakistan, which has become an increasingly unfriendly and unreliable American ally.

In a briefing to reporters before Obama’s speech, a senior administration official said, “We don’t see a transnational threat coming out of Afghanistan.” The threat, he said, “has come from Pakistan.”

It is no coincidence that Osama bin Laden was killed in Pakistan or that he had possible connections to some in the intelligence community there. It’s also no coincidence that most high-level al-Qaida targets are based in Pakistan.

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If Pakistan is the main event, though, it doesn’t make it any easier to figure out what to do there.

In the aftermath of the Navy SEALs attack in Abbottabad, the relationship has grown even rockier.

According to reports, Pakistan may no longer allow American drones to be launched against al-Qaida from what is widely believed to be a secret base within Pakistan. This would be a serious setback, and the best replacement for that base would apparently be in Afghanistan.

That’s why you can expect Americans will leave a significant force in Afghanistan — perhaps as many as 25,000 troops — even after 2014, at which point Obama says most American combat troops should have left the country.

But what is increasingly difficult for the Obama administration to explain is why the Afghan side-show remains the U.S. military’s main event.